Dynamometer control system



Nov. 3, 1942; R. w. PORTER DYNAMOMETER CONTROL SYSTEM Filed June 2'7, 1940 Inventor: Richarq W. Por er. by 7/ His ttorney.

Patented Nov. 3, 1942 UNITED STATES I PATENT OFFICE 2,300,900 v nrnmomaraa coN'mor. srsirnu Richard W. Porter, Schenectady, N. Y., assignor to General Electric Company, a corporation or New York Application June 27, 1940, Serial No. 342,744 H 18 Claims. (CI. 73-51) I This invention relates to electric dynamometers andmore particularly to a system for controlling electric dynamometers employed for testing the performance and efliciency of prime movers, such for example, as internal combustion engines of the automotive and aircraft types.

It is an object of my invention to provide a new and improved electric dynamometer control It is another object of myinvention to provide a control system which automatically adjusts the excitation of the dynamometer to maintain accurate speed regulation at any desired speed under varying conditions of load imposed by the engine under test.

It is a further object of my invention to provide a field-current control arrangement of adjustable character, which after being adjusted to a given setting, automatically maintains con stant field excitation on the dynamometer irrespective of changes in the resistance of the dynamometer field winding due to temperature variations and irrespective of fluctuations in the electrical source of supply from which the excltation current is derived.

It is another object of my invention to provide an improved electric dynamometer control syster whereby control may be transferred smoothly and quickly from one regulating function to the other regulating function and without the use of switches and the like.

It is a further object of my invention to provide means for obtaining a smooth variation in the dynamometer field current from zero up to normal when the dynamometer is being started 5 from rest as a motor in order that a smooth torque may be obtained.

It is another object of my inventionto pro'vide a'dynamometer control system with adjustablespeed.

n; is still another object arm invention t 4:, provide an improved dynamometer control'system which prevents overloading of the dynamometer beyond a predetermined value oi armature current and which shall be operative with thedynamome'ter operating either as a motor rent or the speed of the dynamometer when it is operating either asa motor to drive the engine under test or asa generator to constitute a load for the engine.

It' is another object of my invention to provide a control system which is adapted to control the operation of an electric dynamometer when it is being used in conjunction with an auxiliary loading device.

In carrying out certain tests on prime movers, and particularly internal combustion engines of the automotive and aircraft type, it is customary to couple a dynamoelectric machine with the engine under test and to operate the machine as a power absorption generator for converting the mechanical energy developed by the engine into electrical energy and delivering the same to suitable current translating or consuming devices or to a source of electrical supply. Furthermore,

it has been customary to supply the dynamoelectric machine with current from an external source of supply to operate it as a motor for the purpose of cranking and running-in the engine to overcome its initial stiffness and for makingfriction tests. In such cases the dynamoelectric machine may bea simple direct-current machine of the cradled" dynamometer type having its field frame trunnioned in bearings and free to rotate except as restrained by a scale. The torque deliveredby or to the apparatus under test is transmitted to the field frame by electromagnetic interaction of the rotor and field current. Or, if desired, the field frame of the dynamoelectric machine may be mounted rigidly, and its input energy, or its output energy to a consumption circuit or device measured in a conventional way by suitable means such as a wattmeter.

The present invention relates to a system for controlling the operation of the dynamometer.

0 Incarrying my invention into eifect in its preferred form, the field winding of the dynamometeris excited from an alternating current circuit through a full-wave rectifier including a pair of electric valv'es. In a modification the field winding of the dynamometer is energized by an exciter in the form of a dynamoelectric amplifier of the armature reaction excited type having a control field winding. An electronic regulator or control system acts automatically to vary the conductivity of the rectifying valves or to control the current transmitted to the control ilcld winding of the dynamoeleetric amplifier, as the case may be, in accordance with variations in the dynamometer speed thereby changing the dynamometer field current to maintain constant speed pointed out in the appended claims.

under varying conditions of load. A manual control device provides means for adjustingthe setting or changing the standard of operation of the regulator to regulate for different predetermined dynamometer speeds regardless of changes in the load imposed by the engine under test.

Under certain conditions of operation it is often desired to have the speed of the dynamometer vary in accordance with the torque. The invention therefore contemplates as part of the same control system means whereby the field current of the dynamometer is maintained substantially constant irrespective of fluctuations in the source of supply and changes in resistance of the field 1 which can be produced. Thus,-each regulating function may be used to act as a safety limit for the other.

During certain operating conditions, were it not for certain safety features, the dynamometer might become overloaded either when operating as an absorption generator with the speed regulator in action or as a motor to drive the engine under test. Accordingly, my invention contemplates the inclusion of means which act in response to the dynamometer armature current for modifying the action of the speed or field regulating elements under certain conditions so as to prevent the dynamometer armature current from exceeding a maximum adjustable predetermined value. direct-current dynamometer operating either alone or in conjunction with additional manuallycontrolled loading apparatus.

My invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be In F18. l of the drawing'I have illustrated an electronic control system arranged in accordance with my invention for controlling the operation of an electronic-exciter which excites the field of a dynamometer of the direct-current generator or motor type employed for testing an internal combustion engine. which the electronic exciter of Fig. 1 is replaced by a dynamoelectric amplifier of the armature reaction-excited type.

Referring to Fig. i of the drawing, in order to illustrate the principles of my invention. I have diagrammatically shown a prime mover II in the form of an internal combustion engine mechanically connected to a dynamometer II. The electric dynamometer II which is capable of acting either as a direct current generator or motor comprises a rotatable armature l2 and a separately excited field winding ii. The dynamometer armature terminals ll are adapted to be connected by means of a switch I! to a direct current power system II so that with the dynamometer acting as a generator mechanical energy developed by the engine ll may be converted into electrical energy in the armature l2 and pumped back into the supply lines l8. On the other hand, energy may be supplied to the armature i2 from the system I! when the dynamometer is operating as a motor to drive the engine under test. If desired, by maintaining the switch i5 in the open position, the dynamometer when acting as a generator may be connected by closing a switch it to a consuming device such as a loading resistor II to dissi-' pate the absorbed energy in the form of heat. The resistor I! may also be employed 'as a starting resistor during the period when the dynamometer is being brought up to speed as a motor. A manually controlled variable contact I! provides means for inserting any desired portion of the resistor I! in the dynamometer armature circuit. Connected also in the dynamometer armature circuit is a resistor 20, the function of which will be later explained. The field frame of the dynamometer may be rigidly mounted and its output or input measured by means of a wattmeter in the usual manner. However, I prefer to employ a conventional cradled dynamometer by mounting the field frame in bearings and opposing its rotation by the customary scale beam. These arrangements for the torque measurement, however, are well known to those skilled in the art, are not a part of my invention, and, therefore, are omitted for the sake of simplicity in the description and drawing.

In certain applications a very large torqueabsorption capacity is required to fully load the engine under test. It being impracticable in such cases to build dynamoelectric machines such as H of adequate capacity, I may provide an additional loading device such as either an hydraulic dynamometer or an eddy-current dynamometer 2|. In the arrangement illustrated I have shown a dynamometer of the latter type having a rotor 22 mechanically connected to the engine under test and a field winding 23 connected in circuit with a variable resistance element 24. The field The load limit device is operative with the Fig. 2 shows a modification in winding 23 may be energized from any suitable source of direct current and in the illustrated embodiment I have shown it arranged to be connected to the source of supply l8 through a switch 25. The two dynamometers may conveniently be mounted on a common base and with their rotors 'l2 and 22 coupled together. The stators or field frames supporting the windings l3 and 23 are also preferably strapped rigidly together by a pair of torque-transmitting frames (not shown) and the combined torque reaction may be measured on a single beam scale or automatic scale in either direction of rotation. The torque reaction on the scale is thus the net torque delivered by or to the combined unit.

The shaft 28 to which the prime mover il is connected drives the armature 21 of a small electric tachometer or pilot generator 28. the generated voltage of which varies in direct proportion to the speed at which its armature member is rotated. A permanent magnet 29 provides the necessary excitation fiux. I wish to point out that while I have shown a pilot generator of the direct current type, it is not my intention to limit the invention in this respect. For example, an alternating current generator and a rectifier may be employed if desired.

The field winding ii of the dynamometer is excited by an electronic amplifier including an alternating current circuit 30 and a full-wave rectifier arrangement comprising a transformer 3| and electric valves 32 and 23. The primary winding of the transformer is connected "to the source of supply 30 through a switch 34 and a asoopco transformer 3i.

The electric valves 32 and 33 may be of any of the several types well known to those skilled in the art, but I prefer to use rectifying valves of the vapor electric discharge type in which a main discharge takes place between the anode and cathode only during each half cycle of the supply current when theanode is positive with respect to the cathode, and in which the particular point in' the cycle of the anode voltage at 2" I which the current starts to flow in the valve is determined by the potential on its control electrode, but in which the current once it starts to flow through the valve may be interrupted only by reducing its anode potential below the a critical value.

It 'should be understood that the electronic exciter' just described may be of the polyphase v p and thus be energized froma polyphase source of supply, as will be clear to those skilled so in the art.

In order to control the output oi. the electronic exciter arrangement-and thereby the amount of current flowing in the field winding I 3-1 have provided a phase shifting circuit comprising a 35 bridge 45 having resistance elements 45 in two opposite arms and having capacitors 41 in the other opposite arms. One conjugate portion 01' the-bridge 45 is connected across a secondary winding of which is adapted to be connected to the alternating current circuit through the switch 34. The other conjugate portion of the bridge 45 is connected to the control electrodes through current limiting impedances, such as resistance elements 50, while the common cathode connection 5I of these two valves is connectedto the electrical midpoint 52 of the secondary winding 48 through a circuit includin conductors 53 and 54, a resistor having im- 9 pressed thereacross a substantially constant pote'ntial, a resistor 55 having impressed there- 7 across a potential which varies in a manner to be explained hereinafter, and a conductor 51. A smoothing capacitor 53 is preferably connected 5 in parallel with the bias resistor 55 to serve as a means of. absorbing extraneous voltage variations. In certain cases it may be desirable to 7 connect a small capacitor 59 between each of-th' control electrodes and the cathode of the valves '32 and 33, respectively. The screen grid 39 of each valve maybe' joined directly to .the common cathode connection 5|. 1

The valves 32 and 33 have a critical grid or control voltage below which they will not begin 5 to pass current even though their anode voltages are positive. Since with the foregoing arrangement the alternating component of the voltage applied tothe control electrodes 33 lags the potential applied tov the anodes 35 by an angl'e oi 79 approximately 90 electrical degrees, the valves are prevented during each cycle from passing current until the anode voltage has progressed through an appreciable part of its positive half cycle of variation. Furthermore, by varying the direct current component of the control voltage corresponding to the net voltage appearing across resistors 55 and "55, this point in the cycle at. which the valves begin to pass current may be advanced or retarded. so as to control the average value of the current flowing between the anodes and the cathodes. This variation of the direct or continuous component of the control voltage has the eflect of shifting the alternatin component plus or minim so that corresponding values of potential will be obtained earlier or later in the cycle. I

Before energizing the anodes oi the valves 32 and 33 it is desirable to allow a short period of time for the heating of the cathodes 31 by their heater elements 45. These heater elements are adapted to be connected to a secondary winding H: of the transformer 45 and are thereby supplied with alternating. current from the source of supply 3| upon closing the switch 34.

These connections are not shown in order to avoid confusion in the drawing. The timing relay 35 prevents energization of the primary winding of the transformer 3| until the cathodes are heated to their operating temperature.

In order to provide a constant source of reference voltage, I employ a suitable arrangement, such as a rectifier circuit. which may comprise a secondary winding I of the transformer 43..

a full-wave rectifier element 5| connected to the winding 50, a suitable filter arrangement pro.-

vided in the output circuit comprising a reactor L and capacitors C,:and a resistor 52 and glow discharge device 53 connected in series circuit relation across the positive and negative direct current terminals 54 and 55, respectively. Variations in voltage across the terminals 54 and Y 55 will not materially alter the voltage across the x glow discharge tube 53, but these voltage variawinding 48 of a transformer 49, the primary m tions will appear across the resistor 62. The voltage across the tube 83 is impressed on the resistor 55.

The substantially constant voltage which appears across the resistor 55 atpoints 55 and 55 serves as a reference potential for comparison with different voltage components varying in accordance with certain characteristics or conditions to be controlled. One condition is the speed of the dynamometer; another is the field current of the dynamometer. An electronic regulator." is provided for variably energizing the resistor 55 in the control circuit in accordance with these conditions. To make the description clear, it is pointed out that the field current regulating minimum value of field current which the speed regulating element can produce. In a similar manner, the speed regulating function is ineffective when the field current regulating function "is in operation except to determine the maximum speed which the current regulating element. can

produce.. That is, the electronic regulator 51 maintains the speed of the dynamometer ii at a I substantially constant value so long as the current transmitted to the field winding l3 remain greater than a predetermined permissible minimum value,-and under certain conditions, if desired, so long asthe armature current transmitted to or by the armature I! does not exceed a predetermined maximum value. If the iield current required to maintain thedynamometer ,at'this constant speed becomes less thanthe predetermined minimum value the speed is permitted to vary and the minimum value of fleldcurrent is maintained. If the maximum value of the armature current is exceeded while the dynamometer is operating as a motor the dynamometer excitation is increased, and if it is exceeded when the dynamometer is operating as a generator'the excitation is decreased, without regard to the speed, and the maximum value of armature current is maintained.

The regulator 41 operates in a similar manner to maintain a constant ileld current on the dynamometer II, when it is desired to allow the speed to vary with the torque, so long as a predetermined maximum speed is not exceeded. If

while the motor is connected across the line, and

the possibility of complete field removal caused by faulty operation of any part of the regulator is less with the present connection. Second, resistor 5i necessarily has a very high resistance, such as for example, a megohm. There is some slight possibility of erratic operation if a tube and socket, which might have a comparable value of leakage resistance, be connected across it.

The regulator 81, as stated hereinbefore, includes a system for transmitting variable amounts of unidirectional current through the resistor to control the conductivity of the electric valves 32 and 33 in response to the above described controlling influences. To this end I employ an electric valve means I having anodes i9 and 10, a common cathode 1|, and a heater element 12. This valve through its two conducting paths serves as a means for smoothly and quickly transferring from speed to held current control, and vice versa. without the interposition of mechanical switches and it also serves the purpose of automatically transferring the control from field current to speed regulation at a predetermined maximum speed and from speed to field current regulation at minimum field current. Furthermore, as will be later explained, the field current and speed regulator actions may be modified by means including this valve when a predetermined maximum current in the armature Ills exceeded.

The tube or valve 88 may be any one of the seva predetermined cathode 1|, the cathode potential will be essentially the same as that of the more positive anode and will be independent of the other anode. As will be understood from the foregoing explanation of the theory of operation of the tube 84, if one of the anodes, such as 69, is connected to be energized in accordance with speed variations of the dynamometer and to such a value that it is more positive than the anode 10, the potential across the resistor 56 will be controlled in accordance with the speed variationsand the regulator 61 will regulate speed. Similarly, if the anode 10 is connected to be energized in accordance with field current variations and to such a value that it is more positive than the anode 69, the potential variations across the resistor 56 will be controlled in accordance with field current variations and the regulator 61 will regulate the field current in the winding ii. To this end, that is for selectively controlling the conductivity of the two electronic paths of the valve means 68, I provide a pair of electric circuits energized by means including the direct current circuit having terminals 64 and 65. 1

Consider first the circuit which is employed for carrying out the speed regulating function. This circuit includes a serially connected impedance element such as a resistor 13 and an elec- "tronic amplifying device or valve 14. .The valve ""15 preferably of the high vacuum type and comprises an anode 15, a cathode 16, a control electrode 11, preferably screen and suppressor grids 18 and 19 respectively, and a heater element 80. A capacitor 8|,the function of which will be explained hereinafter, is shown connected between the control electrode 11 and the cathode 516. -The suppressor grid 19 is connected directly to the cathode 16, while the screen grid 1! is eral types of double-dioderectlfier tubes, such for example, as a hot cathode bi-phase high vacuum pure electron discharge type rectifying tube. I wish to call attention to the fact that, while I prefer to employ the arrangement shown, if desired, and within my invention, I could just as well employ two tubes of similar characteristics with their cathode electrodes connected together. Furthermore, the anodes may be connected together instead of the cathodes by rearranging the control potentials. Such modifications are shown and claimed in the Livingston Patent 2,109,352, assigned to the same assignee as the present invention. The characteristics of the valve II are such that current will flow to the cathode 1! only from that one of the anodes I! and 14 having the higher positive potential with respect to the cathode, so that if a high resistance such as It is connected in series with the connected to the anode 15 through a capacitor 82 and to the positive terminal 66 of the direct current supply through a resistor 83. The series circuit including the resistor 13 and the principal electrodes 15 and 16 of the valve 14 are connected tothe positive and negative terminals 84 and 65 respectively of the direct current source of supply. The anode 89 of the transfer valve 88 is connected at 84 to the anode 14 and resistor 13. Thus, the resistor 56 is connected in parallel with the amplifier or valve 14 through the anode i9 and the cathode 1| ,of the valve 68.

The common juncture 84 between the resistor,

13 and the anodes 15 and 69, rises and falls in potential depending upon the conductivity of the valve 14. For example, the voltage from anode to cathode of the valve 14 and, therefore, that across the resistor 55, is reduced to a very low positive value when theanode current is a maximum, because of the large potential drop through the resistor 13. This voltage rises as the anode currentof the valve 14 decreases, the potential of the point 84 approaching as a limit the potential of the positive terminal 64 of the source of supply.

The direct current component of the bias voltage connected between the common cathode connection II of the valves 32 and 33 and the midpoint 51 of the transformer winding 48, as already explained, includes a substantially constant negative potential derived from the resistor 55 and the serially connected opposing potential derived from the resistor 56. When the potential across the resistor 56 is a minimum, the fixed potential across the resistor 55 biases the control electrodes 38 of the valves 32 and 33 with a direct current voltage'which is negative with 9,800,960 respect to their associated cathodes 81, thereby voltages.

I shall now describe the apparatus employed for energizing the control electrode I1 of the that the control electrode 11 is energized in accordance with the difierence between two normally opposed voltage components, one of which remains substantially constant and the other of which varies in magnitude substantially in proportion to the dynamometer speed.

Movement of the adjustable connection or contact 88 of the potentiometer toward the right from the position shown,'or toward the negative terminal 88a, has the eifect of setting the regulator for a higher speed inasmuch as the valve I4 is thereby made to pass more current which amplifier 18 with an electrical quantity which varies in accordance with speed variations of the dynamometer II to produce proportional amplified variations in the potential across the resistor 56. In accordance with the arrangement disclosed, variations in the potential of the control electrode 11 with consequent variations in the amount of current delivered to the field winding I3 are brought about by a control which depends for its operation on the difference between a constant reference voltage and a speed-dependacross a voltage divider or potentiometer 86 and a series resistor I11, so that these two elements combined have impressed upon them the full voltage generated by the pilot generator 28. v

By means of a section 88 of the resistor 55, a

' fixed component of the constant glow tube voltage is derived to serve as a reference or standard for comparison with the variable voltage of the pilot generator. The negative lead 85a from the 1 pilot generator is connected to the control electrode 11. A manually controlled variable contact or connection 88 of the potentiometer 88 is connected to the positive end of the resistor section 88 through an adjustable portion 'of a variable resistance 88. The negative end of the resistor section 88, which" is connected to the negative terminal 65, is electrically connected to the cathode 16 of the valve 18 through the common negative bus or lead 85m I wish to point out that while I have shown invariable means'88 for deriv-' ing the reference voltage, an adjustable potentiometer may be employed, if desired, so that manually adjustable voltages may be obtained but which will nevertheless remain constant for any setting of the potentiometer.

The resistance element 88 with its adjustable contact 8| forms part of a stabilizing device, the

operation of which will be more fully described I to the dynamometer armature circuit through a transformer, it will be clear that its energization depends upon the rateof change of current in the dynamometer armature and consequently a correction is introduced into the circuit of the .control electrode" which isproportional to this rate of change. This corrective factor-introduced into the control circuit effectively prevents hunt- .ingthus stabilizes the operation of the system. 7

when the regulator is being employed to reguilatefthe dynamometer speed, neglectingthe ef .iect of the stabilizingdevice, it willthus be seen causes a lower. positive biasing potential across the resistor 58 and therefore a lower current in the control or field winding I8. Consequently, if the dynamometer is operating as a motor it speeds up, as will be understood by those skilled in the art, and also, if it is operating as a generator, a reduction in its field current tends to decrease the dynamometer output or the load on the engine resulting in an increase in speed. Thus the maximum speed setting corresponds to the condition when the contact is moved all the way to the right. Conversely, movement of the contact 88 to the left sets the regulators for a lower speed.

Consider now that portion of the regulator amplifying device 88 which may be identical to the valve I4 and which has its corresponding electrodes identified by like reference characters.

The suppressor grid 19 is connected directly to .1

the cathode 16. The screen grid I8 is connected respectively to the positive conductor 68a of the direct current source of supply through a resistor 88, to the anode 15 through a capacitor I88, and to the cathode I6 through a resistor Ill. The anode l5 and the cathode 16 are connected in a circuit including a source of potential derived from the resistor 82 which may be traced as follows: Positive terminal 68, conductor 88a, resistor 81, anode I5, cathode I8, conductor I88, field resistor II, common cathode'connection II, conductors 58 and 58, and the less positive direct current terminal 66. The anode 18 of the valve 88 is connected to the anode 18 of the valve 88 through a resistor I88 and to the negative conductor 88a through a resistor I88. Thus the resistor 88 is connected in parallel with the resistor I85 through the anode I8 and the cathode 'II of the-valve 88. I p

The point I88 at the juncture of the resistor 81 and the anode I5 of the valve 88 rises and falls in potential in accordance with the degree of conductivity of the valve 88. For example,

the point I88 is maintained at a relatively high potential when the anode current. in the valve 88 is very small but becomes less positive as the anode current increases due to the drop in potential through the resistor 81. Consequently, at low values of current through the valve 88, the resistors I88 and I85 will have relatively high potentials impressed upon them so that the potential at anode ll of valve 88 will rise to a relatively high positivev value, causing the voltage to rise across the biasing resistor 56 to effect an increase in the fiow of current in the field winding I8. Conversely, higher values of current through the valve 88 cause thepotential at the point I88 and the anode l8 to become less positive thereby decreasing the voltage across the resistor 56 provided the speed does not become so high that the voltage on anode i9 is higher than that on anode Ill, and causing a decrease in the dynamometer field current.

The input electrodes, that is, the cathode 16 and the control electrode 11 of the amplifying valve 90 are energized in accordance with the difference between a constant reference voltage of adjustable value derived from the resistor 55 and a voltage which is variable in accordance with the dynamometer field current. A component of the constant glow tube voltage is obtained by connecting a potentiometer or voltage divider I08 across a section I09 of the resistor 55. Adjustable amounts of the potentiometer voltage obtained by a manually adjustable contact or connection IID are connected in opposition to the variable voltage appearing across the field resistor ll by a circuit including conductor I03, resistor ll, conductor 53, potentiometer I08, conductor III, and a resistor H2.

It will be seen that movement of the adjustable contact III) to the right increases the negative direct current bias voltage on the control electrode I1 of the valve 98 and the eifect will be to set the regulator for an increased field current. Conversely, movement of the contact IIII to the left from the position shown produces a smaller negative bias so that. the regulator is set for a lower field current, the minimum value of field current corresponding to the condition when the contact H is moved all the way to the left.

With the anodes 69 and III of th transfer valve 88 connected as shown it will be seen from the foregoing description that by means including the two electronic conductive paths of the electric valve 68 the conductivity of the electric valves 32 and 33 may be controlled selectively from that circuit of the speed responsive and field current responsive circuits which produces the predominating voltage or control potential on the respective anodes 69 and 10. Under normal operation, by moving the adjustable connection or contact IIII toward the left or positive end of the potentiometer I08, the potential on the anode I0 may be lowered to such'an extent that the anode 69 will always be more positive throughout a wide speed range, and the regulator will regulate speed so long as the speed regulator does not attempt to reduce the field current below the minimum value corresponding to the setting of the contact H0. When such a condition arises the anode Ill becomes more positive than the anode 69, so that the field current regulator assumes control and the dynamometer, field current is maintained at the value corresponding to the setting of the adjustable contact III), the speed being permitted to vary at will. Similarly, by moving the adjustable contact 89 toward the right or negative end of the potentiometer 86, the potential on the anode 89 may be lowered to such an extent that the anode I0 will always be more positive throughout a wide range in values of field current, and the regulator will regulate the field current so long as the contact H0 is not set at such a value as to .cause the speed to rise to a higher value, than that dictated by the setting of the adjustable Kine does not cause the dynamometer speed to exceed the speed setting of the adjustable contact 89. When such a condition arises the anode 69 becomes more positive than the anode III, with the result that the speed regulator assumes control, and the dynamometer operates at a maximum speed corresponding to the setting of the adjustable contact 89, the field current being permitted to vary at will. The foregoing operations may take place with the dynamometer operating either as a generator or as a motor.

In some cases, if there were no safety device the dynamometer I I might be greatly overloaded causing serious damage. This is particularly 'true in the case where a large engine is being tested by means of a comparatively small eapaclty direct-current dynamoelectric machine such as I I operating in conjunction with a larger hydraulic or eddy-current loading device. The larger unit in such case absorbs most of the power, but the smaller direct-current dynamometer takes up variations in the total power in such a way as to hold the speed constant. Under such conditions of operation there is always the danger that the regulator will drive the small direct-current dynamometer to dangerously high values of armature current in attempting to maintain the speed at a constant value ii, for example, the load taken by the large loading unit or dynamometer is suddenly changed or the engine fails. Inthe latter event the dynamometer would tend to operate as a motor to drive the larger unit. Accordingly, I provide means for modifying the action of the speed regulator to reduce automatically the field excitation of the dynamometer whenever the armature current exceeds a predetermined safe maximum value in the generating direction, until the armature current falls to the predetermined maximum value or until the field current is reduced to the minimum value as determined by the setting of the adjustable contact III. Conversely, if the armature current becomes too large in the motoring direction the action of the speed resulator is modified to increase automatically the fieldv excitation of the dynamometer until the armature current drops to the predetermined maximum value. Therefore, the eifect of this load limiting function of the regulator so far as the overall operation of the system is concerned is to keep the armature current within limits, plus and minus, irrespective of the setting of the speed regulator for the respective generating and motoring actions.

In the arrangement illustrated, this comprises an electric valve means I I 3 preferably of the high vacuum, high amplification, twin-triode type having a pair of electric discharge paths including anodes Ill and III, cathodes Iii and Ill, and control members or grids H8 and H9, respectively. Although the electric valve means H3 is shown as being of the type in which both electric discharge paths are enclosed within the same envelope, it is to be understood that I may employ a pair of electric discharg path which are each mounted within a separate envelope, and that the cathodes thereof may be connected together. The cathodes Iii and III ar joined together and their common point is connected by a conductor I2. to a manually adjustable contact or connection I2l of a potentiometer or balancing resistor I22. The potentiometer III is connected in series circuit relation with a resistor I23 across the positive and negative conductors 64a and 6511, respectively, leading from the direct-current source of supply.

The anode III is connected to the anode I of the. transfer valve 68 by means oi a conductor I 24. The conductive path including the anode m and the cathode m is thus energized from the direct-current source of supply by a circuit 1 which may be" traced as follows: positive line contact'I2I of potentiometer I22. The anode III is connected by a'conductor I25 to the juncture I25a of the control electrode Tl of the lectric valve 98am} the resistor 2. Thus the conductive path including the anode Hi and the oathode III is energized from the direct-current source of supply by a circuit which may be traced as follows: positive terminal 64, resistor 62, conductor 84, the active portion of potentiometer I08, contact IIII, conductor III, resistor II2,

' tential drop across resistor 20. The valve H3 including the two conductive paths is preferably normally biased somewhat beyond cut-of! by means of the potential applied to the common cathodes from the potentiometer I22 which pocurrent becomes excessive to reduce the field excitation to a value sufficient to prevent the armature current-from exceeding the predetermined maximum value or until the field current is reduced to the minimum value as determined by the setting of the contact Ill. 'In other words, the

righthand conductive portion may reduce the field excitation up to the point at which the potentials of the anodes 69 and II become substantially equal, under which condition the potential across the biasing resistor 56 will be equal to that across the resistor I05. As will be clear the potential across this resistor and the anode III is determined by the field current and by the set ting of the adjusting member III.

If the armature current becomes excessive in the motoring direction, the control electrode H9 becomes more positive and the lefthand conductive portion including the anode II! and cathode II I begins to pass current. Since this current flows through the resistor II2, the control electrode II of the electric valve 92 is thus made more negative relative to the cathode I6 causing this valve to pass less current. This reduction in current flow through the valve 98 increases the voltage across the resistors III. and I05 so that the potential on' the anode ll of the transfer valve 68 is increased. Consequently, the positive biastential biases these cathodes positively'relative to the control electrodes H8 and H9. The juncture I28 of the control electrode Ill and the resistor I26 is connected by the conductor 94 to one side of the resistor 20 in the armature circuit of the dynamometer II, while the juncture I25 of the control electrode H9 and the resistor I2! is connected to-the other side of the resistor 20 by the conductor 95.

As will be clear to those skilled in the art, with a given field current and direction of rotation, when the dynamometer is operating as a motor its armature current, and, consequently, the current in the resistor '20, will fiow in one direction and when the dynamometer is operating as a generator its armature current and the current in this resistor will flow in the opposite direction. Consequently, one of the control electrodes Ill and I I9 will be made more positive (or less nega tive) with respect to the common cathodes H6 and I H for generator action of the dynamometer, while the other control electrode will be made more positive (or less negative) for motor action.

Assume thatfor generator action the armature current flows through the resistor 20 in a direction such that the left end of the latter to which the conductor 94 is connected is more positive than the right end to which the conductor 95 is connected. The control electrode I I8 is thus made more positive with respect to its cathode I I6, while the control electrode II! is made more mg potential across the resistor 56 is increased with the result that the firing point. of the valves '82 and 33 is advanced and he current flowing in the field or control winding Ilof the dynamometer is increased until the armature current drops to the predetermined maximum value. It will thus be seen that either theaction of the speed "regulator and the pilot generator or the action of the field current regulator may be modified in negative with respect to its cathode III. The

converse is true for the dynamometer operating as a motor. Consequently, with the speed regulater in action, if the armature current through vthe resistor 20 becomes excessive in the gent er-- ating direction, the righthand portion of the valve IIS'including the anode III and the oathode IIB becomes conductive. fiows through the resistor 13 and in so doing will lower the potential on the anode 69 of the transfer valve 58, decreasing the positive biasing potential across the resistor 56, with the result that the firing point of the valves 32 and 33 is retarded and the. current flowing in th control or field winding I3 is reduced. The action of the speed Current therefore that the dynamometer is operating either as a generator delivering its output energy to the supply Sy tem I6, or as a motor receiying its input energy from the system I6. Under such conditions, and as an illustration, if a surge takes place on the system IS, the result is a rapid rate of change in the dynamometer armatur current with corresponding changes in speed. I provide stabilizing or damping'means including the variable resistance element I, referred to hereinbefore, for limiting the rate of change of the dynamometer armature current or preventing the armature current from changing too suddenly.

In accordance with the arrangement illustated, the resistance element 90 is connected to the secondary winding 96 of the transformer 92, and the primary winding 93 is connected across' the armature resistance element 20 as already explained.. With this arrangement it will be clear that the voltage induced in the secondary winding 96 and thus the potential impressed on the resistance element 90 are dependent upon the rate of change ofthe current flowing in the resistor 20. The slidable variable shunt resistance SII with contact 9| provides means for changing the amount of the voltage Induced in the secondary coil 96 which is introduced into the control regulator will thusbe modified when the armature circuit of amplifier II. The shunt resistor may be replaced by a potentiometer, if desired, but I prefer to employ the arrangment shown inasmuch as failure of the contact OI would be billzing means Just described anticipates a change in speed which would otherwise take place due to the sudden change in the armature current and acts on the control electrode TI of the amplifying valve 14 before the pilot generator voltage has had time to undergo an appreciable change. Thus, if there is a positive rate of change in the armature current in the generating direction of current fiow, the resulting potential difierence in the shunt resistor 90 is impressed on the control electrode 11 in a positive direction to cause a corresponding reduction in the current in the control or field winding II. In other words the voltage introduced into the input circuit by the stabilizing device is in the same direction as would be the change in the pilot generator voltage, if the latter only had sufilcient time to become effective. Similarly, a sudden negative rate of change in the armature current will produce an increase in the current flowing in the field winding ii. The damping means thus anticipates and prevents rapid changes in speed caused by the regulater or any part of the electrical system. The device operates in a similar manner for armature current fiow in the motoring direction.

The capacitor ll which is connected between the control electrode I1 and the cathode 16 of the amplifying valve 14 partially filters out extraneous effects due to torque pulsations from the engine, commutator ripple, and poor contact at the brushes of the pilot generator. In addition, any rapid fluctuations in the voltage -applied to the control electrode 11 tend to become amplified in the plate circuit of the amplifying valve H and are coupled back in an opposing manner on the grid 18 by means of capacitor 82 in such a way as to oppose the original eifect of the control electrode 11. By means of the foregoing arrange ments small transients in the pilot generator volt age are prevented from producing corresponding transients in torque. In other words the openation is slowed down Just enough so that the operator is enabled to obtaina reasonably steady torque or power indication.

Although the actions of the stabilizing device and of the capacitors 8| and 82 are similar in that both tend to prevent rapid torque fillctllflm tions, they are different in that the stabilizing device tends to make the regulator correct more rapidly for deviations in speed caused by the electrical system, whereas the filtering action of condensers BI and 82 always makes the regulator respond more slowly. The latter may therefore cause continued'oscillation or hunting, if used alone, but the former will prevent it. Although it is not always necessary I prefer to use both of these devices simultaneously, as shown.

In explaining the complete cycle of operation of the embodiment of my invention shown in Fig. 1 of the drawing, it will be assumed that it is desired to start the dynamometer II from rest as a motor to drive the engine II. For this condition,

.it is necessary to be able to apply field current to the dynamometer independently of the speed regulator action. Therefore, at standstill the field-current regulator always takes control and any desired field current can be maintained. To start the dynamometer as-a motor the speed control arm I! is preferably moved to the right or toward a maximum speed position thereby giving the field regulating element full range of control. The switch 34 is closed to energize the various heater elements l0, l2, and II, through transformer windings Hi and Hz, and the other resulat'or elements. With the switch II in the open position and the contact or adjuster I! moved to the right, the switch I is closed The armature current at standstill is limited by the resistance II to a normal value.

Assuming that weak-field starting is being employed, the torque is smoothly and gradually increased during the starting period by increasing the field current which results when the field current adjuster III is moved to the right. As the dynamometer begins to rotate fromstandstill resulting in a corresponding decrease in armature current, the resistor I! may be cut out of the circuit by moving the adjuster I! to the left. To transfer to speed control the contact or speed rheostat arm 89 is moved to the left or in the direction corresponding to reduced speed until the speed actually begins to decrease or the field current to increase. This indicates that the speed regulating function has taken control and corresponds to the condition when the left-hand anode 68 of the transfer valve I8 is more positive than the right-hand anode 10. Full range of speed control is then obtained by adjusting the contact or field rheostat arm Ill to the left or to a desired minimum field setting. So long as the field current does not fall below this minimum,

the speed will be held constant by the speed regulator. To transfer back to field current control the field current adjuster III is moved to the right until a reduction in speed is observed. This indicates that the field regulating function has taken control. The speed regulator contact 89 is then moved to the right or to a desired maximum speed setting. So long as the field current regulator is not set to produce a field current low enough to raise the motor speed beyond the predetermined maximum set by the speed adjuster '9, it will regulate the field current. Thus during normal operation in the motoring direction, in which the armature current does not exceed the maximum limit, either the field current or the speed may be maintained substantially constant. In the event that the current flowing through the armature ll of the dynamometer tends to exceed a predetermined maximum value, the potential across the resistor 20 rises correspondingly, the anode Iii begins to conduct current, resulting in an increase in the potential of the anode II to increase the dynamometer field current. Thus, regardless of which of the field current or speed regulating functions are in action at the time of an overload during the motoring operation, they become ineffective to regulate during the overload period. In the case of the latter mentioned function, the control exerted by the pilot generator and the speed regulating element becomes ineffective and control is transferred from the anode 6! to the anode II. The stabilizing device operates to limit the rate of change in the armature current as already explained.

As stated previously, the dynamometer II trol winding l3.

. 2,300,960 the engine ill, may be loaded into the resistor ll or its energy may be pumped back into the system II or a motor-generator set. with the dynamometer operating as a motor from the system I. as already explained, by turning on the ignition of the engine I and gradually. opening its fuel .throttle theengine may be made to drive the dynamometer. and cause its .armature-current -to reverse. Further increase inthe input orfuel supply will tend to increase the speed with the result that the regulator it set for speed regulation will increase the dynamometer field current thereby increasing the load to restore the speed to normal. Or it field current regulation is desired, the speed will vary with the torque. The operation of the regulator is'identical when'the dynamometer is loaded on the resistor ll.

To obtain a better understanding of the operating cycle, assume that the dynamometer is operating under equilibrium conditions at a given speed to load the engine it by pumping power into any suitable absorption system such as the system IS, a motor-generator set, or the resistor l1. Under such conditions upon a decrease in the input to the engine N, the dynamometer tends to slow down and the output voltage of the pilot generator becomes less, thereby causing the amplifier 14 to pass more current. This increase in current results in a decrease in the voltage drop tlirough the biasing resistor 56,

thereby causing the control electrodes ll of the valves 12 and 83 to become more negative relative to their cathodes 31. Consequently, the current flowing through thecontrol winding ll of 'the dynamometer is decreased and the dynamometer speeds up until its speed is restored to its former value corresponding to the setting of the adjustable contact 89 of the potentiometer. In a similar manner, it the dynamometer load is suddenly decreased, for example, due to an increase in voltage of the system It or a variatibn in resistance II, or if the input to the engine is increased; tending to increase the dynamometer I speed, the voltage generated by the pilot gen-,-

erator increases, thereby causing the control electrode I1 to become more negative to increase the current delivered to the dynamometer concomes more heavily loaded and it slows down. Should the armature current tend to exceed'the predetermined maximum value for which the contact'arm III is set, the anode III of the valve "3- becomes conductive, the voltage drop through. the resistor It increases, and the anode 09 becomes less positive. Therefore, the potential tions in the field resistance, the resulting decrease in the potential drop in the resistor ll causes the control electrode 11 or the valve 98 to become more negative relative to the cathode 16, with the result that this valve passes less current. The potential at the anode I0 and across the resistor III! are increased with the result that the potential drop through the biasing resistor 56 is increased. Consequently, the valves 32 and 33 pass more current and the dynamometer excitation is resorted to its original value. Similarly, upon-an increase in the dynamometer field current the regulator will operate to restore the field current toits original value.

As a specific illustration of a condi i n n the operation of the device, if the field current ad- Justment is set for one ampere and the speed adiustment issuch that more than one ampere of field current is required, the regulator will regulate speed, because the fleld current anode 10 of the transfer valve 68 will be considerably less positive than the speed 'anode 69. Un-

der these conditions variation of the field from the speed anode, which is gradually becoming less positive, and prevent any further decrease in the field current. It the field current adjustment is now moved in the direction to' raise the field current the speed will drop. The

transfer from speed regulation to field current regulation is complete. To transfer back to speed regulation the field current adjustment H0 is movedin the direction of lower field current until the speed becomes equal to the value called for by the speed adjustment setting, or the speed adjustment could be lowered to the same end. 'At this point the speed anode of the trans- I current anode, and transfer The dynamometer thus bedrop through the resistance element 5! decreases.

resulting in a decrease in the dynamometer field current. Themaximum armature current limit means will be eitective to produce a maximum reduction in the field current, i! need be, up to the point when the potential of the anode I has been lowered a suiiicient amount to make it equal to that of the anode 10. Since, the potential oi the anode I. is determined by the setting oi the adjustable contact or field rheostat arm I II, it will thus be obvious that itls the adjustment of this setting which determines the minimum field current which can be produced under such conditions. for generator action in a manner similar to that alreadydescribed.

When the apparatus is field current, with the speed regulator adjusted to its maximum-speed position, ir-there is a reduc- The stabilizing device operates employed to regulate a fer tube 88 becomes more positive than the field takes place automatically.

7 It will be seen that with the minimum field current limit feature below which the speed regulator becomes ineffective, the possibility of loss of torqueand stalling the engine in the case of transient speed dips is avoided. Similarly,

- when the regulator is regulating field current the speed regulator acts as an over-speed limit, which can be set at any desired value. Only a very small change in the bias voltage impressed on.

the control electrode oi the amplifier I4 is necessary to obtain full range of field current'on the dynamometer. The speed regulator is thus very sensitive to slight speed changes and acts to increase the field current on a slight overspeed and reduce it on a slight underspeed. Such an action will tend to hold the speed -constant for resistance-load, pump-back, or motor operation. By means of the overload-limit protective feature, the excitation of the dynamometer is reduced automatically whenever the armature, current exceeds a safe value in the generating direction and increased automatically whenever the armature current becomes too large in the motoring direction. This feature. however, does not affect the over-all operation except to keep the armature current within limits, plus in the genllll will afiect neither rection.

When the relatively small dynamometer II is being employed in conjunction with the larger unit 2I for testing large engines the regulator operates in the same way as already described. In this arrangement the larger unit has its field winding 23 energized from the system I5 and its energy absorption rate is varied by adjusting the field rheostat 24. The larger unit thus absorbs most of the .power and the dynamometer II takes up the variations in power in such a way as to maintain the speed at a substantially constant value. Thus by gradually varying the rheostat 34 any desired load within the combined capacity of the two dynamometers may be imposed on the engine under test.

In Fig. 2, in which like reference characters represent corresponding parts, I have shown a modification in which the exciter of Fig. 1 com prising an amplifier of the grid-controlled rectifier type is replaced by an exciter in the form of a dynamoelectric amplifier I30 of the armature reaction-excited type. Certain features of the dynamoelectric amplifier I30 are disclosed and claimed in a, copending application of E. F. W. Alexanderson and M. A. Edwards, Serial No. 281,008, filed June 24, 1939. and which is assigned to the trainee of the present application. Such a dynamoelectric amplifier is known as an amp ldyne. Referring to Fig. 2, the dynamoelectric amplifier I30 is shown mechanically connected to a suitable constant speed driving means, such as a motor I3I, which for convenience, may be energized from the alternating current system 33. The amplifier I30 comprises a control field winding I32, an armature winding I33, and is further provided with two sets of brushes, one act of which includes brushes I34 and I35 which are short-circuited through a conductor of low resistance and provide a path for the short-circuit current which produces one component of the exciting fiux of the machine. The other set, comprising brushes I38 and I31, provide an electric power output which is amplified relative to the power supplied to the control field winding I32. The output terminals of the amplifier, I36 and I 31, are connected to the field winding I3 of the dynamometer by means of a circuit which preferably includes a compensating field winding I33 and a resistor H which is similar to the corresponding element of Fig. 1. Inasmuch as the magnetomotive force of armature reaction produced by the output current is on the same magnetic axis as that produced by the control circuit, but oppositely directed, there exists a strong back-coupling efiect between the two circuits. The principal effect of this back coupling is to reduce the sensitivity or amplification of the device, but under certain conditions it may also act to cause instability or oscillations. The com ensating winding provides a magnetomotive force, which opposes and substantially reduces the nor mal armature reaction in the direct axis of the amplifier and thus serves to neutralize the back coupling.

The amplifier I30 may also be provided with a quadrature-axis or cross field winding I33 which is shown connected across the output terminals I30 and I31 through a suitable resistance element I40. This winding is not absolutely necessary in the functioning of the system but has the advantage of reducing the current in the short circuit axis including the brushes I34 and 2,300,960 crating direction and minus in the motoring diheating in the amplifier. In addition, the dynamoelectric amplifier I30 may be provided with a second control field I which is adapted to produce a magnetomotive force in opposition to that of the first control field, I32, and which is connected in shunt with the dynamometer field winding I3 and in series-circuit relation with a suitable resistance element 42. The field winding I is likewise not an indispensable element in the operation of the system but it serves to reduce theeflects of residual magnetism in the amplifier I30 and aids in bringing the minimum obtainable value of field current more nearly to zero.

Fundamentally, the dynamoelectric amplifier I30 may be considered as a two-stage amplifier incorporated in a single machine, the first stage of amplification being from the control field winding I32 to the short-circuited brushes I34 and I35 and the second stage being from the short-circuited brushes I34 and I35 to the power or output brushes I36 and I31. The power input to the control field winding I32 of the dynamoelectric machine I30 is thus greatly amplified and this amplified output power is employed for variably energizing the field winding I3 of the dynamometer II. This arrangement thus provides a high ratio of amplification combined with a quick and accurate response.

The control field winding I32 may be energized in accordance with the potential appearing across the conductors 53 and 51 in a manner similar to that in which the control electrodes 38 of the valves 32 and 33 01 Fig. 1 are energized. In such case the control field I could be adjusted to aid the excitation produced by the control field I32 since the net voltage across resistors 55 and 55 can be made to go negative if necessary in order to overcome the eiiects of residual magnetism in the dynamoelectric amplifier. However, if a control system is desired which demands a greater ratio of power amplification than is obtainable in the dynamoelectric amplifier I30 alone, there may be introduced an additional stage such as an electronic amplifier I43. This amplifier includes an electronic valve I44 preferably of the high vacuum, high amplification, type comprising an anode I45, a cathode I46, a control electrode I41, a screen grid! and a suppressor grid I49. The output electrodes I45 and I45 may be energized from a suitable source of supply I50, such as a storage battery, or they may be energized by the rectifier and filter combination which is connected to the points 04 and 85, but for various reasons, I prefer to employ an independent source of supply. The screen grid I45 is connected to the positive terminal of the source of supply I50 through a resistor I5I and it is connected to the cathode I48 through a resistor I52 and a selfbiasing resistor I53. The input electrodes of the amplifier I43, including the cathode I40 and the control electrode I41, are connected by means including conductors 53 and 51 to be energized in accordance with the diiierence between the voltages across the resistor 55 and the resistor 53,

v which voltage diflerential is dependent upon variations in the characteristics to be regulated or controlled as will be appreciated from the foregoing description in connection with the appsratus of Fig. 1. It will be further appreciated that the resistance element H which is connected in circuit with.the field winding I3 perand therefore serves to reduce the losses and forms the same function as does the corresponding element shown in Fig. 1 and described hereinbeforc.

. ulator.

asoopeo In view of the description in connection with Fig. 1 it is believed that a detailed description of the operation of the apparatus of Fig. 2 is unnecessary. It seems suilicient to state that the potential drop through the resistor '6 as determined by the electronic regulator 61, controls the excitation of the control field I32 and thus the dynamometer field l3 to maintain the speed of the dynamometer at a substan a constant adjustable value so long as the armature current transmitted to or from the armature II of the dynamometer does not exceed a predetermined maximum value and so long as the field cur-r second regulating device responsive to the field current of said machine for maintaining said rent, as evidenced by the drop in poten-' tial through the resistor H, is not reduced below a predetermined minimum value. If

- the armature current tends to exceed the maximum value, the speed of the dynazmometer ii is permitted to vary and the maximum value of dynamometer armature current is maintained. 0n the other hand, if the armature current is not exceeded but the field current tends to become reduced ,below' the predetermined minimum value, the speed is .permitted to vary and the minimum value of field current is maintained. As explained in connection with Fig. 1, the apparatus is also adapted to regulate the field current of thedynamometer in which case the speed is permitted to vary with the torque.

The apparatus of my invention incorporates the highly desirable features of an electronic resfield current substantially constant, means for setting said field current regulator to hold a predetermined value of field current, and means responsive to values of field current greater than -said predetermined value for rendering said speed regulating device effective and said current regulating device ineffective and responsive to said predetermined value of field current for rendering said current regulating device effective and said speed regulating device ineffective."

3. In combination in a testing device, a prime mover to be tested, a dynamoelectric machine having an armature and a field control winding and adapted to be mechanically connectedto said prime mover, means for absorbing energy from said dynamoelectric machine, means for variably energizing said field winding to maintain the speed of said prime mover substantially constant,

a and means responsive to the armature current of Its lack of inertia and its high amplification factor combine to provide high sensitivity and close regulation, simplicity of operation, maintenance of the same degree of sensitivity, and freedom from excessive maintenance. Heretofore', all data involving speed required timed runs, lasting often fromthirty seconds to two minutes, in order to obtain accurate speeds. The aparatus of this invention reduces the speed variable to a constant and thereby effects aconsiderable saving in time. It is readily adaptable to operation at various speeds and field current values. It has the further advantage of so controlling the dynamometer that power may be pumped back into the power system with stability thereby effecting a considerable saving'in the cost of the testing operation. Furthermore, by virtue of the arrangement for rapidly transferring from load to friction runs in the engine testing operation, loss of time resulting in objectionable cooling in the engine cylinders is avoided.

While I have described the principle of operation of my invention, together with the apparatus which I now consider to represent the best embodiments thereof, it will be obvious to those skilled in the artthat modifications and varia tions may be employed in carrying out the invention, and I aim therefore to cover all such modifications and variations as fall within the scope of my invention as defined in the appended claims.

What I, claim as new and desire to secure by Letters Patent of the United States, is.

1. A control system for a. dynamoelectric machine having an armature and a field winding comprising in combination, means responsive to the speed of said machine for varying the energization of said field winding to maintain the 7 speed of said machine substantially constant, a second regulating device responsive to the field current of said machine for maintaining said field current substantially constant, and means responsive to a predetermined valueof said field said dynamoelectric machine for modifying the action of said second mentioned means for ad- Justing the current in said field control winding to'limit said armature current to a maximum predetermined value irrespective of speed variations of said prime mover. 1

4. In a device for testing prime movers, an electric" generator including field and armature windings and adapted to be coupled to a prime" mover to be tested, means for absorbing the power output of said generator, means for variably energizing said field winding to control the torque on said prime mover, regulating means responsive to the speed of said generator for controlling the energization of said field winding to maintain the speed substantially constant, means for modifying the action of said regulat ing means to limit the armature current of said generator to a predetermined maximum value, and means for modifying the action of said regulating meansto control the minimum degree of energization of said field winding.

5. In a device for testing prime movers, a

dynamoelectric machine having field and armature windings and adapted to be mechanically connected tothe prime mover under test, said dynamoelectric machine beingv arranged in an electrical circuit to operate as a motor for driving said primeimover or as a generator toloadsaid prime mover, means for energizing said field winding, means responsive to the speed of said dynamoeletric machine for controlling said field energizing means to maintain the speed of said dynamoelectric machine substantially constant during either motor or generator operation, means responsive to the armature current in the motoring direction of said dynamoelectric machine for modifying the action of said speed regulating means to limit said current to a pred'e- 7 termined maximum value, and means responsive to the armature current in the-generating direction for modifying the action of said speed reggenerator operation.

ulating means to limit said generating current to a predetermined maximum value.

6. In a device for testing prime movers, a dynamoelectric machine having field and armature windings and adapted to be mechanically connected to the prime mover under test, electrical circuit means whereby said dynamoelectric dynamoelectric machine when operating as a.

motor for modifying the action of said speed responsive means to limit said motoring current to a predetermined maximum value, means responsive to the armature current of said dynamoelectric machine when operating as a generator for modifying the action of said speed responsive means to limit said generator current to a predetermined maximum value, and stabilizing means for modifying the action of said speed responsive means to counteract the effect of sudden armature current changes on the speed of said dynamoelectric machine for either motor or 7. In a device for testing prime movers, an electric dynamometer having an armature winding and adapted to be mechanically connected to the prime mover under test, electrical circuit means whereby said dynamometer is capable of operating either as a motor for driving said prime mover or as a generator for loading said prime mover, means for controlling the torque of said dynamometer, means responsive to the speed of said dynamometer for energizing said torque controlling means whereby the torque of said dynamometer is varied to maintain its speed substantially constant during either motor or generator operation, means responsive to the armature curnent of said dynamometer when operating as a motor for modifying the action of said speed responsive means to limit said motoring current to a predetermined maximum value,

means responsive to thearmature current of said dynamometer when operating as a generator for modifying the action of 'said speed responsive means to limit said generator current to a predetermined maximum value, and stabilizing means for modifying the action of said speed responsive means to anticipate changes in the,

dynamometer speed of said 8. In a system for testing rotary devices. a dynamoelectric machine provided with field and ar mature windings and adapted to be mechanically coupled with the rotary device to be tested, electric circuit means associated with said armature winding. means for energizing said field'winding to produce torque between said field and armature windings, a regulating element comprising the other while said testingsystem is in operation.

9. In a system for testing prime movers, a dynamoelectric machine provided with field and armature windings and adapted to be mechanically coupled with the prime mover to be tested, electric circuit means'connected to said armature winding adapted to deliver energy to or absorb energy from said dynamoelectric machine, means for energizing said field winding to vary the torque produced by said dynamoelectric machine, a regulating element comprising means responsive to the speed of said dynamoelectric machine for controlling said field energizing means whereby the speed may be maintained substantially constant, a second regulating element comprising means responsive to the field current of said dynamoelectric machine for maintainingsaid field current substantially constant, means for smoothly transferring effective control from one of said regulating elements to the other while said testing system is in operation, said field current regulating means being adapted to limit the minimum field current which said speed regulating element can produce when the speed regulating function is -in operation, and said speed regulating element being provided with means to limit the maximum speed which said field regulating element can produce when the field current regulating functionis in operation.

, 10. In a system for testing prime movers, a dynamoelectric machine having a field winding and an armature for producing torque in either direction, said armature being adapted to be mechanically coupled to the prime mover under test, means for exciting said ,field winding, a first regulating means including means responmeans responsive to the speed of said dynamoelectric machine for controlling said field energising means whereby the speedmay be maintained substantially constant, a second regulating element comprising means responsive to the field current of said dynamoelectric machine for maintaining said field currentsubstantially constant, and means for smoothly transferring eifective control from oneof said regulating elements to sive to the speed of said dynamoelectric machine for controlling said exciting means to vary the torque exerted by the field upon said armature in order to maintain the speed substantially constant under varying conditions of load, and a second regulating means including means responsive to the current in said field winding for controlling said exciting means to maintain said field current substantially constant, said first and second regulating means having electronic means associated therewith whereby effective control may be smoothly transferred from one of said regulating means to the other while said system is in operation. 1

11. In a system for testing prime movers, a dynamo-electric machine having a field winding and an armature for producing torque in either direction, said armature being adapted to be mechanically coupled to the prime mover under test, means for exciting said field winding, a first regulating means including means responsive to the speed of said dynamoelectric machine for controlling said exciting means to adjust the torque exerted by the field upon said armature in order to maintain the speed substantially constant'under varying conditions or load, inductive means associated with the circuits of said armature and said first regulating means whereby the action of said regulating means is modified to counteract the eifect on. the speed of sudden changes in the current in said armature. a second regulating means including means responsive to the current in said field winding for controlling v said exciting means to maintain said field current smoothly transferred from one of said regulat ing means to the other while said system is in operation.

12. In a system for testing internal combustion 1. an electric dynamometer having field andarmaturewindingsandadaptedtobe mechanically coupled to the-engine under test, said dynamometer being adapted for connection in an said valve means, a second electric valve'means having an input and an outputcircuit, means for substantially constant, means for smoothly and selectively transferring control from one of said regulating means to the other while said dynamometer. is in operation, means responsive to the armature current of said dynamometer in the motoring direction for modifying the action of said speed or field current responsive means to limit said armature current to a predetermined maximum value, and means responsive to the generating direction for modifying the action of said speed responsive means to limit said armature current to a predetermined maximum value.

13. In combination in a device for testing internal combustion engines and the like, a dynamoelectric machine having a field winding and an armature for producing torque, said armature being adapted to be mechanically coupled to the engine under test, means for exciting said field winding, electronic means comprising a pair of electrodes a potential which varies in accordance with the speed of said dynamoelectric machine, means for impressing on the other of said free electrodes a potential which varies in accordance with the current in said field winding, and means energized in accordance with said derived potential variations for controlling said field exciting means, whereby the excitation of said field winding is selectively controlled from that one of said energizing said input circuit in accordance with variations in the current in said field winding, an electronic valve comprising a pair of anodes and a common cathode, said electronic valve having the'characteristlc that current flows to .the cathode only from that anode which is maintained at thehigher positive potential, means whereby one of said anodes is subjected to potential variations determined by the flow of current in the output circuit of said first valve- -means, means whereby the other of said anodes is subjected to potential variations determined by the fiow of current in said second valve means, an impedance element connected in said common cathode circuit for deriving a potential which varies in accordance with the conductivity of said transfer valve, and means for impressing said derived potential variations on the input circuit of said amplifier, whereby the energization of said field winding is controlled from that circuit which produces the predominant potential on I said respective anodes, and means associated armature current of said dynamometer in the with the respective input circuits of said first and second valve means for changing their standards of operation, the adjustment of the means associated with said first valve means serving to limit the maximum speed of said dynamoelectric machine when said transfer valve is being controlled from said second valve means, and' the adjustment of the means associated with said second valve means serving'to limit the minimum field current of said dynamoelectric machine when said transfer valve is being controlled from said first valve means.

15. In combination in the device for testing internal combustion engines and the like, a dynamoelectric machine, having a control field winding and an armature for producing torque, said armature being adapted to be coupled to the engine under test, means including an amplifier having an input circuit for exciting said field winding, electr'onc means including a pair of electronic conducting paths each including anode and cathode electrodes, one of electrodes being electrically common to each electronic path and said other electrodes being electrically free with respect to each other, said electronic means having the characteristic that only that path having the greater potential diflerence between its respective electrodes becomes conductive, means for impressing on one of said I free electrodes a potential which varies in acpotential impressing means which maintains the predominant potential difference between the re- I spectiv'e electrodes of its associated discharge .path.

14. In combination in a device for testing prime movers, a dynamoelectric machine mechanically connected to said prime mover and capable of operating either as a motor or as a generator. a

field winding for said dynamoelectric machine, a

power system, means for connecting the armature of said dynamoelectric machine to said power system, means for energizing said field winding and including an amplifier having an input clrcuit,- a pilot generator for producing a voltage proportional to the speed of said prime mover, a first electric valve means having an input and an output circuit, means connecting said pilot generator voltage in the input circuit of cordance with the speed of said machine, means for impressing on the other free electrode a potential which varies in accordance with the field current of said machine, and means associated with said common electrode circuit and the input circuit of said field exciting means whereby said exciting means is controlled from that one of said means connected to the respective free electrodes which produces the predominant potential difference relative to said common electrode,-

16. In a system for testing internal combustion engines, an electric generator for loading said engines including a field winding, a pilot generator, said generator being adapted to be chanically coupled to an engine to be tested, an

- amplifier having an input and an output circuit,

means connecting said field winding in the output circuit of said amplifier, means connectin S id pilot generator to the input circuit of. said amplifier, whereby said fleld winding is.energized to regulate the speed oi said generator, means associated with said amplifier for changing the standard of operation to provide regulation over a wide speed range, and means associated with ment and an armature winding, said rotary element being adapted to be mechanically coupled to a prime mover to be tested, an amplifier having an input and an output circuit, means for controlling the torque on said dynamometer to regulate the speed thereof, said torque controlling means being energized in accordance with the output current of said amplifier, a pilot generator connected for obtaining a voltage proportional to the speed of said dynamometer, means connecting said pilot generator in the input circuit 01 said amplifier whereby said control means is variably energized to change the torque of said dynamometer, means associated with said amplifier for changing the standard 0! operation to provide regulation over a range in speed, and means associated with the input circuit of said amplifier for stabilizing the operation of said system to prevent oscillationor hunting.

18. In combination in a device for testing prime movers, power absorption means coupled to said prime mover and having a control winding whereby a load oi'controllable power-speed characteristics may be imposed on said prime mover, a control field winding ior said absorption means, means for exciting said field winding and including an amplifier having an input circuit, a double-anode vacuum tube, a first means for impressing on one of the anodes of said tube positive potentials which vary in accordance with the speed or said absorption means, a second means for impressing on the other anode of said tube positive potentials which vary in accordance with the current in said control winding,

an impedance element connected in circuit with said tube and subject to potential variations dependent upon the conductivity of said tube,

means for impressing said potential variationson the input circuit or said amplifier to control the fiow 01 current ln said field winding, and means for determining which of said first or second means shall exert eflective control, said means being adjustablewhereby either speed orregulation may be obtained field current throughout range. I RICHARD W. PORTER. 

